1. Field of the Invention
The present invention relates to an apparatus for controlling air flow in semiconductor clean rooms for manufacturing semiconductor devices and, more particularly, to an apparatus with a shutter attached to the lower surface of a grating installed in the floor of a semiconductor clean room.
2. Description of the Related Art
Semiconductor device production, which is performed in a highly purified, precise and sterile environment, has been made possible by advances in many types of technologies, including cleaning technologies. Cleaning technologies are especially important for improving the quality and efficiency of semiconductor devices.
Cleaning technologies primarily rely on clean rooms to provide a particle-free environment for the production process. Clean rooms are widely used not only in the electronics industries, but also in other industries such as precision instrument manufacturing, chemical production, hospital operations, and food preparation.
The clean rooms used in the semiconductor manufacturing industries are spaces in which the number of particles floating in the air is controlled to be below a predetermined value so that such particles do not contaminate a workpiece. In addition, the temperature, humidity, inner pressure, intensity of illumination, noise, vibration, etc. are also controlled together in clean rooms. To control the number of the particles in the room, clean air is continuously fed into the clean room and waste air is continuously removed through a circulation line. In the circulation line the polluted air removed from the clean room is passed through a filter installed on the inlet of the clean room. In this process, the cleaning may be enhanced by adding a scrubber to the circulation line.
An adequate air flow needs to be maintained to keep the number of particles below the predetermined levels. The proper air flow depends on the capacities of the various filters or cleaning devices installed in the circulating lines, the volume capacity of any pumps, and the volume of the clean room. To control an air flow in the clean room, a grating with a lattice of vents is usually installed in the floor of the clean room and a shutter is attached under the grating.
FIG. 1 is a side view of a conventional apparatus for controlling air flow in semiconductor clean rooms. FIG. 2 is an exploded view of the air flow controlling apparatus of FIG. 1.
As illustrated in FIG. 1 and FIG. 2, the conventional air flow controlling apparatus is composed of a grating 10 and a shutter assembly attached to the lower surface of the grating 10. The shutter has a shutter fixed plate 26, and a shutter moving plate 18 disposed between the grating 10 and the shutter fixed plate 26, so that the moving plate 18 can be moved from side to side as shown by the arrow in FIG. 2.
The grating 10 is made of a plastic or ceramic material having a box shape with a square or rectangular top surface. A plurality of air vents 12 are formed in the grating in a matrix, i.e. arranged in rows and columns. Also, a grating through-hole 14, through which the body of an opening-ratio controlling screw 16 passes, is formed at the center of the grating.
The shutter fixed plate 26 has an open box shape of a predetermined volume with upwardly extending sides 26a, and wing parts 26b, each having a predetermined width, extending outwardly from the top of the upwardly extending sides 26a on all four rectangular sides. The sides 26a have a height of about 1 to 1.5 cm.
A plurality of bolt holes 32 are formed on the wing parts 26b, and the wing parts 26b are attached to the bottom of the grating 10 by means of clamping bolts 34 with lengths closely corresponding to the height, or thickness, of the grating 10. A plurality of openings 28 are formed in a matrix on the bottom of the shutter fixed plate 26. Four guide projections 30 protrude up from the bottom of the shutter fixed plate 26.
The shutter moving plate 18 is flat and has openings 20 formed thereon. The openings 20 on the moving plate 18 have the same shape and number as those openings 28 on the fixed plate 26. Also, four guide slots 22 are formed on the moving plate 18 corresponding to the guide projections 30 protruding up from the shutter fixed plate 26.
A rack 24 is attached at the center of the upper surface of the moving plate 18 such that its grooves, or teeth, are perpendicular to the moving plate. The rack 24 is aligned parallel to the direction that the moving plate 18 moves. The moving plate fits within the fixed plate 26 and rests on the bottom of the fixed plate 26.
The opening-ratio controlling screw 16 passing through the grating through-hole 14, has a head with either a linear groove or cross grooves, and has a body with longitudinal threads that engage with the rack 24. As the screw 16 is turned, the rack 24 and the attached moving plate 18 move.
In the conventional air flow controlling apparatus, the assembly and operation are as described below.
As illustrated in FIG. 1 and FIG. 2, the shutter fixed plate 26 is bolted to the bottom of the grating 10. The shutter moving plate 18 is placed on the inner bottom of the shutter fixed plate 26 such that the guide projections 30 on the fixed plate 26 fit through the guide slots 22 on the moving plate 18. The moving plate 18 is held in place by its own weight. Then, the opening-ratio controlling screw 16 is inserted into the first through-hole 14 formed on the grating 10 such that its thread engages with the teeth of the rack 24 attached to the moving plate 18.
When the opening-ratio controlling screw 16 is turned, the rack 24 and the attached moving plate 18 moves. At one extreme position of the rack 24, the openings 28 in the fixed plate 26 and the openings 20 in moving plate 18 align, whereby the area of intersection of the two sets of openings is equal to the area of the openings on the fixed plate 26. The ratio of the area of this intersection to the area of the openings on the fixed plate is called the opening ratio. When the openings are aligned as just described, the opening ratio is 100%. At the other extreme position for the rack 24, the openings are fully displaced from each other so that the intersection of the two sets of openings has zero area. In this case the opening ratio is 0%. When the opening ratio is near 100%, the shutter is said to be open; when the opening ratio is near 0%, the shutter is closed.
After the grating with the attached shutter is installed in the floor of the semiconductor clean room, the opening-ratio controlling screw 16 is rotated to control the opening ratio of the shutter so that the air flow in the semiconductor clean room can be properly maintained.
Also installed under the floor of the clean room are structures for supporting the clean room facility, e.g., H-Beams, as well as utility-lines for the facility, various kinds of pumps for circulating the air flow in the semiconductor clean room, blowing fans, ducts and cables, etc. So, when the conventional grating with the attached shutter is being installed in the floor of the clean room, the grating may not fit properly in place because those above-mentioned structures may be in the way. To fit the grating into the correct position, the structures disposed under the floor of the clean room first have to be eliminated, replaced, or shifted.
The problems are a result of the combined height of the shutter fixed plate height and the grating height. Large quantities of time and effort are required for installing and repairing the grating with the attached shutter, which decreases operational capabilities and productivity.
A need exists, therefore, for an apparatus for controlling air flow in a semiconductor clean room that reduces the combined height of the shutter and grating.